The elastic hygiene market is a large and fast growing market. Elastic polymers that are able to keep their shape upon deformation (low permanent set) are highly desirable in elastic hygiene articles such as diapers. Styrenic block copolymers (SBC's) have long been the workhorse in this market due to their excellent elastomeric properties at body temperature. There have been attempts to approach the elastic behavior of SBCs in newer polyolefins. Commercial block copolymers (OBC's) such as Infuse™ olefin block copolymers sold by The Dow Chemical Company, and copolymers such as Vistamaxx™ propylene-based elastomers (PBEs) sold by ExxonMobil Chemical Company, are less expensive to manufacture than SBC's but show lower elastomeric performance at body temperature than typical SBC's due to the differences in their molecular architectures. Alone, such OBC's and PBE's have largely been inadequate in elastic hygiene applications.
Synthesized via living anionic polymerization, manufacturers of SBCs can have precise control over the number of blocks and the block lengths with a nearly uniform distribution of molecular weights. The glassy block contains a high ratio of polystyrene and the rubbery block contains a high ratio of polyisoprene, polybutadiene or their hydrogenated versions: poly(ethylene-alt-propylene) or poly(ethylene-alt-butene). This is highly desirable. One problem with such SBCs is their expense. It would be desirable to have compositions that are elastic and deformable like SBCs but at a lower cost.
Relevant publications include U.S. Pat. No. 8,071,681; U.S. Pat. No. 8,052,822; U.S. Pat. No. 7,858,706; U.S. Pat. No. 6,635,715; EP 1 858 942 A1; EP 1 871 816 A1; EP 1 882 715 A1; EP 1 623 822 A1; EP 2 832 171; and WO 2002/066540; and K. Sakurai et al. “Blends of amorphous-crystalline block copolymers with amorphous homopolymers. Morphological Studies by electron microscopy and small angle scattering,” in 37(20) POLYMER 4443 (1996).